In a conventional laser printer employing an electrophotographic system, developer cartridges accommodating toner are detachably mounted in the laser printer.
This type of laser printer may be provided with a new cartridge detection unit for detecting whether a mounted developer cartridge is new and for determining the service life of a developer cartridge found to be new.
One such laser printer that has been proposed is a color laser printer having a detection gear provided on each developer cartridge, a corresponding lever that moves when contacted by the detection gear, a drum unit that can be pulled out of the printer's main casing, and photosensors provided in the main casing for detecting movement of the levers.
In this conventional color laser printer, the developer cartridges are mounted in the main casing together with the drum unit. A motor provided in the main casing generates a drive force that is transmitted to each developer cartridge. The drive force rotates the detection gear so that the gear contacts the corresponding lever, moving the lever to a position protruding from the drum unit. When the photosensor detects this movement of the lever, the color laser printer can determine that the developer cartridge is new based on the detection. The detection gear is a sector gear that rotates a prescribed angle only when the developer cartridge is new and does not move when the developer cartridge is not new.